Electronic switch



March 9, 1937. g, u i I 2,072,993

IEIIZJSGTRON'JIC SWITCH Filed March 30, 1933 Z0 IINVENTOR I BY ATTORNEYPatented Mar. 9, 1937 UNITED STATES PATENT OFFICE ELECTRONIC SWITCHApplication March 30, 1933, Serial No. 663,501

5 Claims.

.This invention relates to electrical switches and more particularly toswitches of this character adapted to make and break an electricalcircuit.

5 In one of its aspects the invention is directed to an electronicswitch or trigger device adapted to operate without detrimental arcingin an electrical circuit with a voltage, applied across the terminals ofthe device, of the order of about 40,000 or more volts and the currentpassing through said device may be 1,000 more or less milliamperes.

In its more specific aspect the invention is an improvement over thedevice illustrated and described in the copending application ofMontford Morrison, Serial No. 596,948 filed March 5, 1932, and assignedto the same assignee as the present invention. 7

The aforementioned copending application de- 20 scribes a circuit whichmay be employed to produce good X-ray photographs of the instantaneousexposure type. The circuit, as illustrated in Fig.6 of the drawing ofsaid copending application,

consists essentially of a condenser, an X-ray tube 25 and a noveltrigger tube all in series with the trigger tube having its grid orcontrol electrode and its cathode connected to an outside source ofpotential whereby the absolute prevention and instantaneous flow ofelectrons from the oath- 30 ode to the anode may be efiected atpredetermined and appointed times.

The novel trigger tube disclosed in said co-' pending application in itsbriefest aspect consists of a therminonic cathode, an anode and a gridor control electrode interposed between the anode and cathode. The gridconsists of a perforated or foraminous cup-shaped element. In theoperation of the circuit heretofore set forth, it is necessary that ameans be employed for charging the grid negatively in order to preventelectrons from flowing from the cathode to the anode and at apredetermined time for charging the grid positively so that theelectrons will flow from the cathode to the anode.

When the grid is positively charged the grid becomes heated due toelectron bombardment. Thus, there is a dissipation of electrical energyat the grid. In order to overcome these as well as other difficultiesinherent in trigger tubes when employed in said circuit, I have providedthe presenvelope having an anode and a cathode appropriately spaced fromeach other and a control electrode of novel operation and designappropriately spaced between the cathode and the anode. With a tube ofthis general construction and embodying my inventionit is practical toprevent the flow of current for an indefinite period of time and at anappointed time to allow the flow of current therethrough, which currentmay be of any desired magnitude at any desired voltage and, as hereinillustrated, as high as 1,000 or more milliamperes at 40,000 or morevolts.

One object of my invention is to provide means that are substantiallyfool-proof and adapted to prevent the passage of current therethroughover a period of time and to allow the passage of current therethroughat an appointed time.

Another object of my invention is to provide a new method for preventingand allowing the passage of electrical energy from a source ofelectrical supply to a load.

Another object of my invention is to provide a new method of preventingand allowing the passage of electrical energy of high voltage and highcurrent values in the X-ray field from a source of electrical supply toa load.

Other objects and advantages of my invention will be readily apparentfrom the following specification and appended drawing wherein:

Figure 1 represents a shortened longitudinal cross-sectional view, withsome of the parts in elevation, of a device embodying my invention; and

Figure 2 represents a cross-sectional view taken along line II-II ofFig. 1 in the direction of the arrows.

As shown in Figure 1, one embodiment of my invention is the illustratedtrigger tube comprising an evacuated enclosing gas-tight dielectricelongated envelope l0, composed-of glass or the like, in the form of abulbous midportion l l with a pair of diametrically opposed elongatedtubular arms I! and I3. Extending within said tubular arms I! and I3,are reentrant dielectric tubes l4 and I5, respectively, having pressesl6 and l1 at their respective ends, located'in the proximity of therespective limits of the bulbous portion I l Located within the envelopel and with the effective portions thereof in the approximate center ofthe bulbous portion of the envelope are spaced parallelly arrangedelectrodes l8, l9 and 20. The pressure of the residual gas within thetube is preferably as low as possible and may be of the order of about10- to mm. of mercury.

The electrode I3 is the plate or anode in the form of a plane smoothsurface disk, having the circumferential outer portion thereof curledupwardly and inwardly towards the anode end 5 of the envelope, and awayfrom the electrodes II and 20 to provide a surface of large radii ofcurvature so as to minimize cold electron emis sion between theelectrodes.

This anode or plate It may be of the desired thickness and composed of arefractory metal, as for example molybdenum, and is supported by anelectrical conductor 2| of molybdenum or the like having one end securedthereto and its outer end secured to the conductor 22. The effectiveanode area is preferably greater and about fifty percent greater thanthe overall area of the cathode 26, hereinafter more specificallydescribed. Between the anode or plate l6 and the conductor 22, a portionof the supporting con- 2 ductor 2| forms an air-tight seal-andsupporting means with the vitreous press l6. Secured to a face of theanode or plate l8, within the periphery of the curled edge thereof bymeans of welded right angle suports or other mechanical means, is

a metallic tubular section 23 composed of molybdenum or the like.

This tubular section 23 extends away from the effective face of theanode l6, surrounds that portion of the anode support and conductor 2|within the envelope, the seal and press l6, and a substantial portion ofthe reentrant tube l4 beyond the press. 0n the inner surface of thatportion of the tube 23 surrounding the reentrant tube are secured springfingers 24 whose outer surfaces bear against the outer surface of-thereentrant tube It. This metallic tubular section 23, due to its peculiarassembly and design, serves as a heat distributor and a shock-absorbingand distributing means to aid in the prevention of anode over-heating,seal impairment due to heat and stray electron bombardment thereof andseal fracture.

Moreover, this particular construction aids in the prevention of generaltube fracture caused by 4 mechanical shocks to which tubes of thischaracter might normally be subjected in the course of practicalcommercial manufacture, manipulation or operation. It also serves toassist in supporting the anode It.

At the cathode side of the tube and forming an air-tight seal with thepress I! are cathode lead-in and rigid supporting wires 26 and 26 havingportions thereof extending exteriorly of the envelope and portionsthereof extending within said envelope. Substantial lengths of the upperfree ends 21 and 26 of the support wires 26 and 26 are bent outwardlyand away from each other and are at about right angles to thelongitudinal axis of the tube. Between said supporting wires and sealedin the press II are, and as illustrated six, rigid supporting wires 26,36, 3|, 32, 33 and 34 composed of molybdenum or the like, and insulatedfrom each other at the press II. The upper portions of these wires arebent away from the longitudinal axis of the tube, with upper portions ofthe wires 26, 30 and 3| bent in a direction generally opposite to thedirecion of bend of the wires 32, 33 and 3 6.

The free ends of these wires are all approximately in the same generalplane, which is substantially normal to the longitudinal axis of theenvelope. Securely mounted by welding or other convenient means to thebent portions at or near the free ends hereof, in a generally zig-zagfash- 75 ion, as shown, with each of its segments being in the samegeneral approximate plane, is the filamentary cathode 26.

The cathode 26 may comprise a tungsten fila ment of appropriate lengthand diameter and has its respective ends secured to the bent portions 21and 26 of the support wires 26 and 26. Because of its composition,length and diameter,

the cathode 20 will provide a thermionic emission therefrom, ofsufficient magnitude to supply the desired comparatively large currentof the order of about 1000 milliamperes, when a potential of aboutseventeen volts is applied between lts terminals from the secondarywinding of a low voltage transformer (not shown) connected to lead-inwires 26 and 26. Moreover, this comparatively large thermionic electronemission is effectively secured at the temperature to which the filamentis raised without any substantial vaporization thereof at its maximumattained temperature due to said voltage being applied between itsterminals.

Spaced from and closely surrounding the thermionic cathode 20 is anopen-ended cup 38 of molybdenum or the like, having an inwardly directedflange with a downwardly extending cylindrical portion integral withsaid flange and having a curled upper end whose edge is away from thefaceof the anode I 6 and in close proximity of the outer surface of thecup proper.

The cup 36 has a base 31 provided with an elongated slot 36 adapted toreceive the rigid support wire 26 and the support wires 29, 36, 3|, 32,33 and 36. The other rigid support wire 26 passes through and is incontact with the base. The support wire 25 may be welded to said base,although this is not necessary because it is sufficiently in contacttherewith, as shown.

The inner wall of the cup 36 is in close proximity of the ends of thebent support portions. Its upper curled edge is above the plane of thecathode and the flange portion extends inwardly and below the edges ofthe bent portions of the support and together with its base serves as areflecting surface for the electrons emitted at the cathode 26.Telescoping the downwardly extending cylindrical portion integral withsaid flange is a metallic tubular section 40 having one end thereoffrictionally secured to said cylindrical portion. This tubular section46, composed of molybdenum or the like, supports the cup, surrounds allof the cathode supporting wires, the press and a substantial portion ofthe reentrant tube beyond the press.

On that portion of the inner wall of the tubular section 46, surroundingthe reentrant tube l6, are secured a plurality of spring fingers 35adapted to frictionally engage and bear against the reentrant tube l6.

The cup 36, together with the cylindrical section 66, serves as a heatdistributor and a. shockabsorbing and distributing means to aid inprevention of seal impairment due to heat and stray electron bombardmentthereof which may ultimately result in seal breakdown. Moreover, -thisparticular construction aids in the prevention of tube fracture causedby mechanical shocks to which a tube of this character might normally besubjected in the course of practical commercial manufacture,manipulation or operation.

It also serves to prevent the electrons emitted at the cathode frommigrating over towards the walls of the envelope and acts to constrainthe electrons in a limited field so that they may approach the anode ina preferred path upon excursion, that is to say, the cup 36 focuses theelectrons emanating from the cathode so that substantially all of themare directed to strike the anode l6.

At the respective ends of the vitreous bulb III are secured terminalcaps 43 and 44 in electrical contact with the respective lead-in wires22 and 25, 26. The vitreous envelope i is of appropriate length so thatthese caps 43 and 44 are remotely disposed from each other to preventspark-over therebetween when a predetermined potential, as for example,a potential of forty thousand volts or more is applied therebetween.

The anode and cathode are preferably so spaced from each other that anydanger of filament distortion or other deleterious effects, such as coldemission or arcing, may be prevented during the operation of the tube atthe high voltages to which it may be normally subjected.

At about its mid-length the envelope has a portion thereof in the formof an elongated closed vitreous arm 50 of appropriate length anddiameter. Ring-sealed therein adjacent the closed end of said arm is areentrant vitreous tube having a plurality of spaced ribs 52. Mountedwithin said reentrant tube are spaced electrically conductive guides 53,54 and 55 maintained in fixed position by virtue of the ribs 52 fittinginto circumferential grooves on the exterior walls of said guides.Adjacent guides 53 and 54 have openings at the approximate centersthereof and are of approximately the same dimensions as thecorresponding dimension of an electrically conductive shaft 56 to which,atone end, is secured an armature 51 in the form of a soft iron core andat its other end is electrically secured the control electrode I6. Allof the guides have openings 56 so that the arm 50 maybecompletelyevacuated.

Located in the space between the guides 54 and 55 and respectivelysecured thereto are a plurality of shock-absorbing springs 6i and 62adapted to take up shocks and relieve the tube from the forces of impactduring the operation of the switch in the manner which will behereinafter described.

The control electrode I9 is essentially in the form of a circular platehaving no openings therein and having a diameter that is at least asgreat as that of the anode and preferably about ten percent greater thanthat of the oathode cup 36. The edges of the control electrode is D arecurled away from the anode so that there will be no cold emissionbetween the anode I 8 and the control electrode IS. The controlelectrode i9 is spaced about one-eighth of an inch from the cathode forthe sake of clearance and is maintained at substantially the samepotential as the cathode and the cathode cup by virtue of an electricalconductor 63 secured to the extension 40 of the cathode cup and to theguide 53.

The distance between the guide plates 54 and.

55 is preferably greater than the diameter of the control electrode l6,and the distance between the guide 53 and that edge of the cathode cupimmediately adjacent thereto is preferably greater than the diameter ofthe control elec-- trode l9.

Located exteriorly of said tube and surrounding the arm 50 are spacedwindings 64 and 65 adapted to magnetize the core 51 whereby the controlelectrode l9 may be actuated away from or towards the cathode for theoperation of the switch.

The cathode 20 may be heated to the desired temperature and apredetermined working potential applied between the anode and cathode.

with these conditions existing when the control electrode I! at the samepotential as the cathodeis in the position shown in Figure 1, andcompletely blocking the mouth of the cup 36, it prevents all of theelectrons emanating at the cathode from traveling to the anode l6. Inthis manner a zero plate current may be maintained.

control electrode I6 is in the position shown in Figure 2.

In this manner the control electrode v be actuated so that there is alarge, substantially unobstructed space between the anode and thecathode and the electrons emanating at the cathode are allowed to travelundisturbed from the cathode to the anode. V

II it is desired to again block the flow of electrons from the cathodeto the anode l6, so that the plate current may again be zero, thewinding 65 is de-energized and the winding 64 is energized to causeactuation of the control electrode 19 towards the cathode cup 36. Thecontrol or .blocking electrode l6 travels and assumes the position shownin Figure 1 so that all of the electrons emanating at the cathode 20 areprevented from traveling-to and reaching the anode l6. When highvoltages are to be applied between the terminals 43 and 44, I prefer toinsulate the coils 64 and 65 from the low voltage supply line. The coilsmay be energized by means of an insulating transformer and a remotecontrol may be employed.

The magnetic windings 64 and 65 may be entirely eliminated and actuationof the control electrode I!) may be accomplished by merely rotating thetube about its longitudinal axis. The force, due to gravity, will causethe control electrode i9 to assume the desired position depending on theposition of the tube.

Instead of having the control electrode is spaced from the cup 36 and ifdesired the elimination of the conductor 63 it is within the purview ofmy invention to have a plurality of electrically conductive tracks orguides secured to and supported by the cathode cup 36 and extending overto the guide 53. These tracks or guides may be so arranged that thecontrol electrode I 9 is in contact therewith and supported thereby sothat when the control electrode is in blocking position, it will haveits bottom face in contact with the upper edge of the focusing anode andcathode and to maintain a zero plate current when the working voltage isapplied between the anode and cathode, and the cathode temperature is atthe maximum required. When it is desired to allow the electrons to passthrough the tube, the trip shutter, which may be completely opened in0.002 of a second, are caused to be actuated so that there is a largeunobstructed space between the anode and cathode which allows theundisturbed excursion of electrons from the cathode to the anode.

This invention is susceptible to a number of modifications and it is toprior art.

What is claimed is:

1. A switch comprising an envelope, an anode, a cathode, focusing meanssurrounding said cathode, and a control electrode therein, said anodeand cathode being spaced from each other, said control electrode beingadapted to maintain a zero plate current while in a blocking positionand to allow the flow of current between the anode and cathode when inanother position, said control electrode being electrically connected bymeans wholly within said envelope to said cathode, said controlelectrode while in blocking position being closely adjacent saidfucusing means and obstructing the electron path between said cathodeand said anode to maintain a zero plate current and means for actuatingsaid control electrode from said blocking position to operating positionfor allowing the establishment of a substantially unobstructed electronpath between the anode and the cathode, said control electrode whenactuated being movable in a direction at an angle to the effectiveelectron path between the anode and the cathode, the space between saidanode and cathode being substantially unobstructed when the controlelectrode is in said second mentioned position.

2. A switch comprising an envelope, an anode, a thermionic cathode,iocusing means surrounding said cathode, and a control electrodetherein, said anode and said cathode being spaced from each other, saidcathode upon incandescence being adapted to emanate electrons, saidcontrol electrode being adapted to maintain a zero plate current whilein a blocking position and to allow the. flow of electrons between saidanode and said cathode when in another position, said control electrodewhen in blocking position being closely adjacent said focusing means andbeing electrically connected to the cathode for mainbe limited only bythe.

taining the same at a potential suillcient to prevent the electronsemanating at said cathode from reaching the anode and when in said otherposition allowing the establishment of an eflective electron path toobtain the desired plate 5 current, the space between said anode andcathode being substantially unobstructed when said control electrode isin said second mentioned position.

3. .A switch comprising an envelope, an anode and a cathode and acontrol electrode therein, said control electrode being slidable andwhen in one position blocking the flow of current from the cathode tothe anode and while in another position allowing the establishment of adesired plate current, means electrically connecting said controlelectrode to said cathode for maintaining the control electrode atapproximately the same potential as said cathode during tube operation,said means being located entirely within said envelope.

4. A switch comprising an envelope, an anode, a cathode and a controlelectrode therein, said envelope having an arm, a plurality of guides insaid arm, a shaft carrying said control electrode, said shaft beingslidably mounted in said guides, means electrically connected to one ofsaid guides and said cathode for maintaining the potential of thecontrol electrode at approximately the same potential as said cathode,said means being located entirely within said envelope.

5. A switch comprising an envelope, an anode, a cathode and a controlelectrode therein, said envelope having an arm, a reentrant stem in saidarm, a plurality of guides in said stem, a shaft slidably mounted insaid guides, and secured to said control electrode carried thereby,means surrounding the cathode for limiting the direction of electronsemanating therefrom, and means electrically connecting said controlelectrode and cathode, said means being located entirely withinsaidenvelope.

CLAYTON T. ULREY.

